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Aircraft Design

To plan aircraft development programmes it is necessary to estimate future trends in air transport for both passenger and freight businesses. The number of aircraft movements is mainly related to the demand for passenger travel. Econometric analysis of historical data shows a strong correlation between world economic growth and the demand for air transport. This confirms that an expansion in business travel and cargo transport are linked to growth in commercial and world trading activity. The...

The final design is shown in Fig. 16.9. The large fuselage cross-section is apparent giving the aircraft a 'stubby' appearance. Data for the final design are shown in Table 16.13. The final design exhibits an operating empty weight ratio of 0.599, the slight increase compared with the baseline design being attributable to the higher wing aspect ratio of the final design. Lift drag ratio is increased to 14.76 with a cruise altitude of 35 000 ft. The time required to climb to the initial cruise...

Aircraft fuel mass has to allow for the design flight profile plus the specified reserves. At this stage it is impossible to calculate each stage of the flight plan accurately. However, an estimate of the cruise L D could be made (Fig. 11.4) and could be used to check the cruise fuel requirement. An assessment of the principal engine characteristic will enable an estimate of the specific fuel consumption to be obtained. A statistical chart such as Fig. 11.8 enables the design range to be...

Increasing component efficiency levels has three basic effects. Thermal efficiency is improved by the direct effect of the improved component efficiencies. The optimum pressure ratio increases as shown in Fig. 9.25. The higher pressure ratio in turn improves the thermal efficiency. The best match of turbine entry temperature and pressure ratio changes. However, higher pressure ratio will result in higher cooling air temperatures from the compressor and therefore more cooling air will be...

The development of civil jet transport configurations has largely been an evolutionary process. Despite the many technical improvements that have been introduced over the past 40 years the wing, fuselage and control surface arrangement of modern aircraft appear little different to the original Comet design (Fig. 3.1). Only the engine installation has changed, from the original buried layout to the podded configurations used today. Even this change has its origins in the successful Boeing 707...

During the initial project work the position of the wing along the fuselage will need to be decided. The chosen location will affect the position of the aircraft centre of gravity. This centre of gravity (e.g.) position will influence the payload loading limits for the aircraft. If the e.g. position of the OEM is too far aft the subsequent loading will be unacceptable for nosewheel undercarriage loading and if too far forward there will be insufficient tail power to balance and control the...

The lift increment for a wing with both leading and trailing edge devices may be estimated from two-dimensional section data using the formula below ACUa&lt ACI (Vpped Sref)COsAHL where ACLmax sectional (2D) lift coefficient increment of the device tapped wing area in flowpath of the device (defined in Fig. 8.9) Sref aircraft gross wing area, the design reference area Ahl sweepback angle of the hinge line of the device - may be approximated to the wing TE sweep (for flaps) or LE sweep (for...

The climb-out requirements have been discussed earlier in the chapter. It was shown that in the various flight segments of the mission a minimum gradient is required in the event of engine failure. We can write, with the small angles involved, (D W) as 1 (L D) . Therefore For a given wing and type of flap the (L D) will be a function of the flap angle. The CLmax will also change with flap angle. A typical relationship of (L D) versus CLmax is shown on Fig. 10.29 where (L D) is that appropriate...

Each of the proposed layouts will be subject to a number of active design constraints. These may arise from airworthiness requirements (e.g. second segment climb gradients), performance specifications (e.g. take-off field length), operational parameters (e.g. turn-round time), or be imposed from external influences (e.g. environmental noise rules). There will also be a number of constraints set by the design manufacturing management team. These may include the definition of available materials...

Engine development has shown a steady increase in cruise fuel efficiency over the years. This is shown on Fig. 9.9 in terms of the improvement in specific fuel consumption. It should be noted that the De Havilland Ghost engine used in the first jet-powered airline (the De Havilland Comet) paid a large price in cruise fuel efficiency compared to the then current piston and turboprop engines to gain the much higher cruise speed. It was not until the introduction of the high bypass ratio turbofans...

Before the new design can be sized it is useful to analyse existing aircraft of a similar specification to determine key parameters such as operating empty mass (MOE) ratio and lift drag ratio. These parameters are then used together with the payload range specification to determine an estimate for the aircraft maximum takeoff mass (MTOM). From this information the wing and tail surfaces may be sized. The performance estimates which lead to the definition of powerplant size can then be made. A...

When the wing area is known, the selection of aspect ratio automatically sets the span loading aspect ratio span mean chord span2 gross area As such it is influential in the generation of drag due to lift. This affects the overall climbing ability of the aircraft and its cruise efficiency. For example, climb performance with an engine failure will have to be guaranteed to meet airworthiness requirements. A wing planform with a low aspect ratio will have significantly more difficulty in meeting...

Senior Lecturer, Loughborough University, UK Formerly Head of Aircraft Performance, Rolls Royce, UK Civil Aviation Authority - NATS Department of Operational Research and Analysis (DORA), UK A member of the Hodder Headline Group LONDON SYDNEY AUCKLAND First published in Great Britain in 1999 by Arnold, a member of the Hodder Headline Group, 338 Euston Road, London NW1 3BH http www.arnoldpubIishers.com Co-published in North America by American Institute of Aeronautics and Astronautics, Inc.,...

With an initial estimate of the maximum take-off mass, the remaining aircraft geometry can be sized. As for the regional jet in Chapter 16, this is principally done by comparison with existing aircraft in the first instance to complete the baseline design. Parameters are then changed later in the process as a result of parametric analysis and trade studies. The next parameter to be chosen is the wing loading. This will determine the wing reference area and has an effect on the aerodynamics,...

In association with this book is a series of data sets which are located on the publisher's web site (www.arnoIdpubIishers.com aerodata). There are five separate sets of data Data A contains technical information on over 70 civil jet aircraft. Data B contains details of over 40 turbofan engines. Data C includes geographical and site data for around 600 airports. Data D defines the International Standard Atmosphere (ISA) and various operational speeds. Data E includes definitions and conversions...

The initial cruise altitude capability will fix the thrust level at the top of climb, but the time to height will also be affected by the thrust ratings at the lower altitudes. This can be an important issue from operational considerations. The ability to climb to altitude quickly may enable the aircraft to take advantage of an air traffic control slot which would be missed by an aircraft with a low climb capability. Such aircraft with limited performance may therefore be subject to delay or be...

One of the principal moving parts on the aircraft is the landing gear. This must be as light and small as possible. It must provide good ride dynamics during taxiing and safe energy absorption at touchdown. Retraction of the units is essential to reduce drag during flight. This places a strong demand for space to house the landing gear, usually at the wing fuselage junction. On many designs the landing gear bay requires separate fairing to enclose the wheels and shock absorber units. A...

This study was undertaken using spreadsheets based on the design methods presented in the first part of the book. The initial specification called for an advanced regional airliner with a capacity of 70-100 passengers. The design brief emphasised the importance of fuel cost to the design as it was felt that in future a 'carbon tax' may be levied on aviation fuel. Initial research identified that many of the current 100-seat regional airliners are simply 'down-sized' variants of larger aircraft....

The main sub-groups of mass (e.g. structure, payload, etc.) may be grouped in several different ways. There appears to be no internationally preferred definition and you may find any of the definitions below quoted in reports and in aircraft data sheets. manufactured empty mass the weight as produced at the factory (i.e. the sum of structure + propulsion + fixed equipment ). delivered empty mass MEM plus mass of standard removable items (i.e. those attributable to particular customer...

The aircraft were then optimised using spreadsheet methods. Figure 18.2 (reproduced directly from the spreadsheet output) shows the variation of gross weight with aspect ratio for each of the designs. The minimum gross weight for single-fuselage aircraft is seen to occur for an aspect ratio of 6.75. This is very close to the values used on the first generation wide-body transports as shown in Table 18.1. This illustrates two points. First, it confirms that early wide-body transports were...

For each of the engine options available, the engine, external drives and accessories, engine controls, engine systems, and engine mounting are described 5. engine systems (starting, fuel, hydraulic, pneumatic, electric) 7. engine lubrication, drains and vents Various drawings will accompany these descriptions showing pipework and block diagrams of the system.

The selection of wing section profile is one of the most important decisions of the aircraft design process. It is extremely difficult to correct a poor choice as the whole of the wing geometry will be based on the chosen wing section co-ordinates. The aerodynamic characteristics of the section will be designed to provide an acceptable compromise between the operational requirements of the aircraft (e.g. high lift drag ratio in cruise, good climb performance particularly in emergency flight...

Once all the component masses are known it is a relatively easy task to determine the aircraft centre of gravity position (Fig. 7.12). It will be necessary to know this Fig. 7.12 Aircraft centre of gravity. Fig. 7.12 Aircraft centre of gravity. position at an early stage of the project design to enable the wing to be correctly positioned along the fuselage on the general arrangement drawing of the aircraft. The standard list of component masses shown in the mass statement can be extended to...

The conclusion from the airworthiness analysis of the aircraft is the issue of a Certificate of Airworthiness (C of A) for the design. This represents an expensive but unavoidable element in the total development of the aircraft project. The C of A is only valid for the design as tested and manufactured by the approved organisation. If modifications to the design are made or if the manufacturing methods or organisation are changed, the C of A has to be re-issued. This will only be done if the...

The next stage in the calculation is to compute the climb performance. The first consideration is the determination of the installed engine data at the various climb speeds and altitudes. Installed engine data is defined as the engine performance after allowance has been made for (1) air and power offtakes and (2) intake losses. The installed engine data for the climb is shown on Fig. 10.18. For this example the climb speeds are 250 kt EAS up to 10000 ft, accelerate to 320 kt EAS at 10000 ft,...

Once the cabin cross-section has been decided, the number of seats across the cabin will be fixed. Dividing this number into the total number of seats in each class gives the average number of rows of seats to be installed. The required cabin length will be related to the leg-room provided for each class. For well designed seats this is related to the seat pitch (see Fig. 5.10). The perception of comfort is directly linked to the seat pitch and the number of seats in a unit (a single seat...

On a modern civil jet aircraft the design lift coefficient will be that appropriate to the cruising condition at the design cruise Mach number. A simple formula Fig. 8.3 Derivation of design lift coefficient. Fig. 8.3 Derivation of design lift coefficient. defining design lift coefficient as a function of basic wing geometry is given in Fig. 8.3 (see also ref. 1). The factor Ca in the above relationship reflects the influence of wing camber on the design lift coefficient. For super-critical...

The prospect of distributing passengers in auditorium-type space has often been used to promote the concept of a flying-wing aircraft, now referred to as the 'blended-wing body' concept. Both Airbus and McDonnell-Douglas have recently shown such layouts, see Fig. 3.8. The main advantage for this layout lies in the potential for increased passenger cabin volume and the associated improvement in comfort level. The designers also point out that the distributed payload will give increased inertia...

The drag and weight information can now be derived as shown (in Imperial units) in Fig. 11.20 and 11.21 respectively. The (profile + wave) drag data is shown at a lift coefficient of 0.5 in practice the drag will need to be adjusted for other lift coefficients. In addition the lift-dependent drag needs to be added and an Oswald efficiency factor of 0.86 has been assumed in this example. This drag and weight data (shown in Imperial units) together with the engine data can now be combined to...

If possible, several different methods should be used to estimate each of the component masses in the equation above. This will give confidence to the prediction and guard against inappropriate use of formulae. When it is impossible to determine the absolute mass of a component (perhaps because insufficient details are available) it is acceptable to use a standardised mass ratio, i.e. Such ratios can be determined from existing aircraft of a similar type to the one under investigation. This...

Speeds are given in Table 10.5. Detailed analysis is shown in Tables 10.6 to 10.9. Table 10.6 Calculation of ground run Table 10.6 Calculation of ground run Distance (m) to engine failure speed Distance (m) travelled in two seconds Table 10.7 Distance from end of reaction time to V, Mean speed during transition is given by Vm (Vi + VLor) 2 Table 10.7 Distance from end of reaction time to V, Mean speed during transition is given by Vm (Vi + VLor) 2 Vm l(V2 -...

The take-off and initial climb are two of the most critical safety phases of the aircraft flight. The combined analysis of both phases is referred to as the aircraft take-off performance. A detailed definition of the airfield limits for the aircraft will be held as part of the Aircraft Flight Manual. In the project design phase the field requirement is regarded as an essential part of the initial specification and as such will directly influence the aircraft configuration (e.g. it may dictate...

The geometry described here for the nacelle installation has been based on the analysis of existing aircraft installations covering the major aircraft manufacturers. It covers two different types of installation (separated and mixed jets) engines with separate jets installed in a pod with separate nozzles for the fan flow and core flow as shown in Fig. 9.13 engine with mixed flows installed in a fully cowled pod as shown in Fig. 9.14. The statistical data used for the analysis shown in Tables...

The selection of taper ratio i.e. tip chord divided by aircraft centreline root chord involves several aerodynamic considerations. A constant chord rectangular planform may be easier and cheaper to manufacture than a tapered wing but it is aerodynamically and structurally less efficient. Aerodynamically an elliptical planform is regarded as ideal because it reduces the tip vortex effect. The geometry of some straight tapered layouts can be shown to approximate to the elliptical shape and...

Each main component of the aircraft wing, fuselage, tail surfaces, nacelles and in the low speed flight phases the flaps and undercarriage must be separately assessed for its contribution to the overall drag of the aircraft.2 It is not sufficient to consider only the wing effects in the estimation of drag. For subsonic civil aircraft the overall drag of the aircraft can be considered under three categories 1. profile drag resulting from the pressure field around the shape and from the surface...

The choice of section profile will dictate the section data used in the assessment of the section maximum lift coefficient. Due regard to the effect of Reynolds number must be given in the process. On a three-dimensional wing with taper, the section maximum lift coefficient will vary along the span due to the effect of reducing Reynolds number. The spanwise variation of lift coefficient will depend mainly upon the spanwise loading as shown in Fig. 8.4. The angle of attack at which the two...

The planform of a wing, for a given gross area, is defined by the geometric parameters, aspect ratio, taper ratio and sweepback. These are shown in Fig. 8.2 a . Many wing planforms incorporate a cranked trailing edge see Fig. 8.2 b . This improves the efficiency of the flap and moves the centre of lift of the wing closer to the centre of the aircraft creating a lighter wing structure. For initial design studies it is sometimes necessary to avoid such complications in the planform geometry and...

Sweepback is mainly used to reduce drag from local flow velocities at or close to supersonic speed. Sweeping the wing planform back allows thicker wing sections to be used and delays the onset of the critical Mach number. An equivalent effect can be shown for forward swept wings but these are intrinsically structurally unstable and therefore need a heavier structure to avoid undesirable aeroelastic effects. The main aerodynamic penalty from sweepback is the generation of spanwise flow over the...